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Mitsubishi Electric and Daikin power consumption

We are looking to install 2-3 ceiling concealed units in a large house. The key problem we have is dynamic range: the cooling/heating requirement can be a low as 1kW and as high as 10kW.

We are looking at units made by Mitsubishi Electric and Daikin and would like to understand the capacity line in the catalogues. Does "7.1 (3.3-8.1)kW" and "10.0 (4.9-11.4)kW" imply the minimum compressor output is 50% of nominal capacity (ie 4.9kW and 3.3kW)? Is it reasonable to assume this translates into minimum power consumption of 2.6kW*50% and 2.0kW*50%?

How can we estimate real min power consumption of an inverter unit? The manufactures only quote nominal power consumption at 7.1 and 10.0kW (I think with an outside temperature of 35 degrees/ 50% humidity). They do publish fan consumption figure of the concealed units but the compressor must consume something while it is idling once the target internal temperature has been reached.

As with conventional split systems... there is another variable: Installation.

How long is the lineset?
Is the outdoor unit above or below the indoor unit?
How far are the indoor units from the outdoor unit?
How far apart are the indoor units?
Add these to the variables in my previous post...

Conventional split systems are vague on specific energy usage also... due to lots of factors that are building specific.

Hint: Purchasing this kind of equipment 'by the numbers' is not a good idea... rather find a contractor who KNOWS what they are doing and listen to their recommendations.

As with conventional split systems: The equipment is secondary to the installation.

The kW power consumption numbers are instantaneous, they doesn't always translate nicely into kWh which is what your electricity company bills you for.

The nice thing about the ductless splits is that they can reduce the heating/cooling capacity to match demand. So when only one ceiling unit is on, then you only need 50% capacity and therefore 50% power.

Are you trying to compare these units to conventional split systems to see if these are worth the extra money... or are you just looking to see if they are big enough for your house?

You can call me Sam

It should be a crime to be a mechanical engineer in San Diego
Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

The kW power consumption numbers are instantaneous, they doesn't always translate nicely into kWh which is what your electricity company bills you for.

The nice thing about the ductless splits is that they can reduce the heating/cooling capacity to match demand. So when only one ceiling unit is on, then you only need 50% capacity and therefore 50% power.

Are you trying to compare these units to conventional split systems to see if these are worth the extra money... or are you just looking to see if they are big enough for your house?

We presently have a similar configuration: outdoor unit (10kW) and concealed internal unit with a fibreglass duct for distribution. There is a gas central heating system so the units are only used for cooling but they are on/off heat pumps and expensive to run. For all the "huha" about SEER and seasonal efficiency, perhaps the EER figure is most relevant in our case.

As to power consumed, I suspect you are right in that you cant take the min cooling output and use the EER to get min power consumption.

But the manufacturers must know the limits: if the unit is oversized for evening use because of daytime needs, what happens? I read inverters save energy buy not starting and stopping but in our case if the min cooling figure quoted is double that needed, there will be a point when the internal thermostat has indicated the target temperature has been reached for some time, even that it has been passed, so would that then result in the unit cycling on /off?

Maybe the datum we really want is the minimum % the compressor can work at. If this was 20-30%, there would be little danger of cycling. Unfortunately, the MEE catalogue seems to indicate 50% and Daikin don't quote anything and the technical support line can only read the catalogue we already have..

Most inverter units can drop to about 20-25% compressor RPM, which translates to about 30-35% capacity on minimum speed. This is however the compressor. The indoor units I think will only dopr ot mayeb 50% capacity as mentioned. For for 10% capacity, they will cycle on and off. Depending on the structure, it would be probably on for 5 minutes and off for 25 minutes at minimum load.

If you really, really want 10%-100% capacity, you need chilled water cooling with some sort of outdoor reset temperature control.

principally is the dynamic range. Can you identify HVAC that can work at 10% (ie cool at 10kW or 1kW)? Most seem to reach 50% at best.

You still haven't explained why your load is unique to all other HVAC loads.

Why is it so important that the system perfectly match the heat gain 24-7-365. Inverter units do an incredible job modulating to achieve capacity control. However at a certain point the most efficient and effective thing to do is simply cycle the unit on and off.

Most inverter units can drop to about 20-25% compressor RPM, which translates to about 30-35% capacity on minimum speed. This is however the compressor. The indoor units I think will only dopr ot mayeb 50% capacity as mentioned. For for 10% capacity, they will cycle on and off. Depending on the structure, it would be probably on for 5 minutes and off for 25 minutes at minimum load.

If you really, really want 10%-100% capacity, you need chilled water cooling with some sort of outdoor reset temperature control.

I spoke with Daikin and Mitsubishi. The Daikin units get to 50% of nominal before stopping. They are inverters but as with any motor, cycling consumes more power than running continuously. If their machines produce 3kW min and the cooling requirement is 1kW, the additional energy consumed in start-stop could be similar that consumed while operating continuously..

Mitsubishi (and Fujitsu) has some units which operate 0,9 to 8kw or 15% nominal. They are a little smaller then what is needed on paper but with zoning they would probably meet intermittent needs.